Motor regulation for strip tension control



g- 16, 1955 R. w. MOORE ETAL 2,715,701

MOTOR REGULATION FOR STRIP TENSION CONTROL Filed Se t/30, 1955 sSheets-Sheet 1 Reference Detector Magnetic Amphfler INVENTORS WITNESSESRaymond W. Moore 8 an ABrthur O. Fitzner.

ATTORNEY Aug. 16, 1955 w, MOORE ETAL 2,715,701

IOTOR'REGUIATION FOR srRIP TENSION comm.

Filed Sept. 30, 1953 3 Sheets-Sheet 2 Aug. 16, 1955 R. w. MOORE ETAL2,715,701

uo'roR REGULATION FOR SIRIP musrou CONTROL Filed Sept. so, 1953 3Sheets-Sheet 3 United States Patent MOTOR REGULATION FOR STRIP TENSIONCONTROL Raymond W. Moore, Snyder, and Arthur 0. Fitzner, Eggertsville,N. Y., assignors to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application September 30, 1953,Serial No. 383,208

16 Claims. (Cl. 318-6) This invention relates generally to tensioncontrol systerns, and it has reference in particular to a tensioncontrol system such as may be used to control the tension of a strip ofmaterial in a strip mill or the like.

The system illustrated was designed specifically for use in a two standtemper pass mill although it will be appreciated that it will be usefulinany system where precise control and regulation of the tension of astrip of material is mandatory such as in the processing of steel,paper, or textiles. In a system of the type shown, the tension of thematerial being processed between the mill stands is of particularimportance. The second stand is the master stand and determines therolling speed. The tension regulating devices for systems of thecharacter contemplated herein such as delivery tension devices andwinding reels can have the strip tension regulated between them bycurrent regulators for regulating the current in their armaturecircuits. The remaining and major regulating problem is the control ofstrip tension between the first two stands. A current regulator cannotbe used on the first stand to regulate the tension between the first andsecond stands since the armature current of the drive motor for thefirst stand is not a correct indication of strip tension. The motorarmature current must supply the friction and rolling losses as well asthe tension load. A regulator which permits fast and accurate control ofthe torque of the driving motor for the first stand to regulate thetension of the strip between the first and second stand is required.Another requisite of the type control system referred to is that thetension regulation be eliminated for threading the mill or at any timethat the strip of material is not operatively passing between thestands, such as when a break occurs.

Accordingly, it is an object of this invention to provide a controlsystem for strip material in a mill which will regulate the tension ofthe strip.

A more specific object of this invention is to provide a control systemfor strip material in a mill which is responsive to a strip tensionsignal to regulate the tension of the strip.

Another specific object of this invention is to provide a control systemfor strip material in a mill which is responsive to a strip tensionsignal only when the strip is operatively passing through the mill.

A still more specific object of this invention is to provide a controlsystem of the character referred to which provides IR compensation forthe armature circuit of the drive motor of the first stand of the millunder normal operating conditions and an increased speed of response ofthe IR compensation for threading operation.

The objects stated are merely illustrative. These and other objects willbecome more apparent from a study of the following specification andaccompanying drawings in which:

Figure 1 shows the systemcontemplated in blockform, and

Figs. 2A and 2B combined show diagrammatically the circuit.

The two stand temper pass mill as shown in Fig. 1 comprises a payoffreel 1, from which the strip of material 2, which is to be processed, isunwound, an entry tension device 3, the first mill stand 4, a tensiondetecting device 5 which is designed to respond to tension of the stripof material 2, the second mill stand 6, a delivery tension device 7, anda windup reel or roll 8. The windup reel or roll 8 is driven by thewinder drive 9 and the strip of material 2 passes from the payoff reel 1between the rolls of the entry tension device 3,v

between the rolls of the first mill stand 4, over the tension measuringdevice 5, between the rolls of the second mill stand 6 and the rolls ofthe delivery tension device 7, onto the windup reel 8.

The delivery tension device drive 10 and the entry tension device drive11 are current regulated to obtain the desired tension between the entryand delivery tension devices and their respective mill stands. Thesedrives are not illustrated in detail since per se they do not form partof the present invention. Information relating to one type of drivesuitable for application to tensioning rolls 3 and 7 may be had byreference to a copending application of A. J. Winchester, Jr., filedAugust 19, 1950, Serial No. 180,405, entitled Tension Control System andassigned to the assignee of this invention. The drive for the secondmill stand 6 con sists of a drive motor 12 and a booster generator 13connected in series with each other and across the main buses 14 and 15.The second stand is the master stand, and the speed of the drive of thesecond stand determines the rolling speed.

The drive for the first mill stand 4 consists of a motor 16 connected inseries with a booster generator 17 across the main buses 14 and 15.Since the motor current of the drive motor 16 for the first mill standmust supply friction and rolling losses as well as the tensioncorrecting torque, the armature current of the drive motor is not a trueindication of the strip tension, and, therefore, current regulationcannot be used to regulate the tension between the first and the secondmill stands. In order to regulate the tension of the strip of material 2between the first and the second mill stands, the ten sion detectingdevice 5 is used. The tension detecting device or tensiometer ispreferably of the double cantilever beam supported type. This detectingdevice has small mass and fast response and can, therefore, followchanges in strip tension accurately. In this device, strip tensioncauses an output voltage to be produced in a detector 18. The voltage isproduced by two movingarmature electromagnetic devices.

A reference voltage and the voltage from the tension detector 18 arematched by applying each to a separate control winding of the firstmagnetic amplifier stage 20. Thus, the output of the first magneticamplifier stage 20 is determined by the difference between the voltagefrom the reference source 19 and the voltage from the tension detector18. Actually it is the magnetomotive forces caused by the referencevoltage source 19 and the tension detector voltage source 18 that arematched rather than the voltages themselves and thus the tension andreference signals are electrically isolated.

The second magnetic amplifier stage 21 has its output controlled inaccordance with the output of the first magnetic amplifier stage 20 andthe current flowing through the impedance 22 which is in series with thearmature of the drive motor 16 for the first mill stand I 4. The outputof the second magnetic amplifier stage 21 supplies the field excitationfor the booster generator, 17 to thus control armature current of thedrive motor 16 for the first mill stand, and, consequently,

regulate the tension of the strip of material 2 between the first millstand 4 and the second mill stand 6. A signal is fed back to the firstmagnetic amplifier stage 20 from the output of the second magneticamplifier stage 21 by the leads 23 and 24 to prevent hunting. Ananti-hunt damping signal is fed back to the first magnetic amplifierstage 20 from an auxiliary field 25' on the booster generator 17. Thesignal which is fed back from the auxiliary field 25 is approximatelyproportional to the rate of change of the output of the boostergenerator 17 and is utilized for damping purposes.

The tension detector 18 also supplies a signal to a magnetic amplifierrelay circuit 26. The magnetic amplifier relay circuit 26 is providedfor the purpose of insuring that the system does not try to regulate fortension when the strip of material 2 is not operatively passing betweenthe first and second mill stands 4 and 6; that is, the system does notregulate for tension when the strip of material is being threaded in themill, or when the strip of material is broken. It may be seen that ifthe system were regulated for tension during the treading process, themotor 16 of the mill stand 22 would be slowed down in an attempt toincrease the tension between the two mill stands. Since the tensionsignal is measured by the tension detecting device 5, the first millstand 4 would continue to slow down within the limits of the regulatorbecause no tension signal would be supplied to the first magneticamplifier stage 20 and the full unopposed reference signal woulddetermine the output of the booster generator 17. Hence, the magneticrelay 26 is provided. The magnetic ampli fier relay 26 picks up therelay 27 when it has an output; that is, when the tension detector 18supplies a tension signal, and thereby connects the first magneticamplifier stage 2%) to its supply source through the contacts 28.However, if there is no tension signal sup plied from the tensiondetector 18, the magnetic amplifier relay 26 will not have an output,and the contacts 28 of the relay 27 will be open to disconnect the firstmagnetic amplifier stage 20 from its supply, and therefore, the systemwill not regulate for tension. Also, the anti-hunt feedback signals fromthe output of the second magnetic amplifier stage 21 and the specialfield 25 on the booster generator 17 will be effectively disconnectedfrom the system, since they are fed back to the first magnetic amplifierstage 20. Thus, the output of the second magnetic amplifier stage 21will cause the drive motor 16 for the first stand 4 to run at a desiredspeed for threading purposes, and an appreciable amount of IRcompensation will be applied to the armature circuit of the motor 16 toprevent stalling. The response of this IR compensation is fast, sincethe damping feedback signal from the special field winding 25 of thebooster generator 17 is ineffective due to the first magnetic amplifierstage 2t) being removed from the system.

The main generator which supplies the system is connected to supply thevoltage between the main bosses 14 and 15. To jog, either in the forwardor reverse directions, a reduced excitation is supplied to the maingenerator which is of the proper magnitude and sense to cause the millstand drive motors to rotate in the desired direction and at the desiredrate of speed. The main generator and the jogging system are not shownsince they are well known in the art and are not considered a part ofthis invention.

The circuit of Figs. 2A and 2B combined shows the system in more detail.A strip of material 2, the tension measuring device 5, the rolls of thefirst mill stand 4 and the rolls of the second mill stand 6 are giventhe same reference characters as were used in Fig. 1. The tensiometer 5has the two moving armature electromagnetic detector heads 36 and 31 tomeasure the strip tension of the material 2 at either side. The outputsof the detector heads 3! and 31 are connected across the input terminalsof the full wave bridge rectifiers 32 and 33, and their outputs aremixed across the resistor 34.

The first magnetic amplifier stage 20 consists of magnetic amplifiers 35and 36, each having its circuits connected in a conventional doublerarrangement. The magnetic amplifier 35 has main windings 88 and 37,anti-hunt damping winding 38, anti-hunt degeneration winding 70,reference control winding 40, tension control winding 41 and a biasingwinding 42. The magnetic amplifier 36 has main windings 43 and 44,antihunt damping winding 45, anti-hunt degeneration winding 46,reference control winding 47, tension control winding 48, and a biasingwinding 49. The main windings 88 and 37 of the magnetic amplifier 35 areconnected in series with saturating rectifiers 87 and 39 and the seriescircuits are connected in parallel with each other. The supply for themagnetic amplifier 35 comprises the transformer T1, which has oneterminal connected between the saturating rectifiers 87 and 39, and theopposite terminal connected to one input terminal of the full wavebridge rectifier 50. The opposite input terminal of the full wave bridgerectifier 50 is connected at a point between the main windings 88 and 37of the magnetic amplifier 35. In like manner, the main windings 43 and44 of the magnetic amplifier 36 are connected in series with saturatingrectifiers 51 and 52 and are supplied by transformer T2. One secondaryterminal of the transformer T2 is connected at a point between thesaturating rectifiers 51 and 52 of the magnetic amplifier and theopposite terminal of the transformer T2 is connected to one inputterminal of the full wave bridge rectifier 53. The opposite inputterminal of the full wave bridge rectifier 53 is connected at a pointbetween the main windings 43 and 44 of the magnetic amplifier 36.

The output terminals of the full wave bridge rectifier 50 are connectedacross the mixing resistor 54 and the output terminals of the full wavebridge rectifier 53 are connected across the mixing resistor 55, andthus the resultant of the voltages from the magnetic amplifier 35 andthe magnetic amplifier 36 appears across the two mixing resistors 54 and55. The bias winding 42 of the magnetic amplifier 35 is connected inseries with the adjusting potentiometer 56 across the leads 57 and 53which carry a D.-C. supply voltage. The bias Winding 49 of the magneticamplifier 36 is connected in series with an adjusting potentiometer 59across the leads 57 and 58. The tension control windings 41 and 48 ofthe magnetic amplifiers 35 and 36 are connected in series with eachother and by the leads 6t) and 61 across the resistor 34 and thusreceive the voltage generated by the tensiometer 5 which is a measure ofthe tension in the strip of material 2.

The tension control windings 41 and 48 are wound such that the currentthat flows through the windings due to the voltage across the mixingpotentiometer 34 drives the core of the magnetic amplifier 36 away fromsaturation or towards cutofif and causes the core of the magneticamplifier 35 to be saturated. The reference control windings 40 and 47of the magnetic amplifiers 35 and 36,

respectively, are also connected in series with each other and across areference source through the adjusting potentiometers 62 and 63. Thereference control windings 4t) and 47 are also wound in opposite senseswith respect to their respective cores; that is, the current which flowsthrough the reference control windings due to the voltage across theleads 57 and 58 as adjusted by the adjusting potentiometers 62 and 63causes the core of the magnetic amplifier 35 to be driven towards cutoffand the core of the magnetic amplifier 36 to be driven towardssaturation. Thus, it may be seen that the effect of the tension controlwinding 41 is in opposition to the effect of the reference controlwinding 40 on the core of the magnetic amplifier 35 and similarly, theefiect of the tenSiQn Control winding 48 is in opposition to the effectof the reference control winding 47 on the core of the magneticamplifier 36. The tension and reference signals are matched by matchingthe effect of their magnetomotive forces on the cores of the magneticamplifiers and 36 of the first magnetic amplifier stage 20.

The first magnetic amplifier stage then operates as follows: The voltageacross the reference windings 40 and 47 is set so that the system willgive a desired tension in the strip of material 2. If the strip ofmaterial is passing between the first and second mill stands 4 and 6,respectively, at a tension which is less than that selected by thereference voltage, the tensiometer 5 Will cause a voltage to appearacross the mixing potentiometer 34, and, consequently, a voltage toappear across the tension control windings 41 and 48. The magnetomotiveforce of the tension control windings 41 and 48 will not be sufiicientto match the magnetomotive force of the reference control windings 40and 47. Therefore, the magnetic amplifier 35 will be driven towardcutoff and the magnetic amplifier 36 will be driven towards saturation.Therefore, the magnetic amplifier 36 will have an increased output whichwill appear across the mixing resistor with a positive polarity at thelower terminal of the mixing resistor 55. If, on the other hand, thetension in the strip of material 2 should be greater than that tensionselected by the reference voltage, the tension control windings would becontrolling and the magnetic amplifier 35 would be driven towardssaturation, while the magnetic amplifier 36 would be driven towardcutofi. Thus, the magnetic amplifier 35 would have an increased outputwhich would give a voltage across the mixing resistor 54 which ispositive at its upper terminal, and, therefore, under these conditions,the resultant voltage across the two mixing resistors 54 and 55 would bepositive at the upper terminal. The elfect of the antihunt dampingwindings 38 and 45 and the anti-hunt degeneration windings 7t) and 46will be discussed later. It will be seen that under steady-stateconditions, the outputs of the magnetic amplifiers 35 and 36 are matchedacross the mixing resistors 54 and 55, and, therefore, the resultantoutput of the two magnetic amplifiers across the mixing resistor iszero.

The second magnetic amplifier stage 21 consists of the two magneticamplifiers 64 and 65, both connected in a conventional doublerarrangement. 'The magnetic amplifier 64 has main windings 66 and 67,connected in series with saturating rectifiers 68 and 69, respectively.The two series circuits are connected in parallel with each other. Themagnetic amplifier 64 also has a bias winding 71, an IR compensatingwinding 72', and a control winding 73.

The magnetic amplifier 65, which is connected in push-pull with themagnetic amplifier 64, has main windings 74 and 75 connected in serieswith saturating rectifiers 76 and '77, respectively. The two seriescircuits are connected in parallel. The magnetic amplifier has a biaswinding 78, an IR compensation winding '79 and control winding 80. Themagnetic amplifier 64 is supplied from the transformer T3 which has oneterminal connected between the saturating rectifiers 68 and 69 and theopposite terminal connected to one input terminal of a full wave bridgerectifier 81. The opposite input terminal of the full wave bridgerectifier 81 is connected between the two main windings 66 and 67 of themagnetic amplifier 64. The magnetic amplifier 65 is supplied from thetransformer T4 which has one terminal connected between the saturatingrectifiers 76 and 77 and the opposite terminal connected to an inputterminal of the full wave bridge rectifier 82. The opposite inputterminal of the full wave bridge rectifier 82 is connected at 'a pointbetween the main windings 74 and of the magnetic amplifier 64.

The drive motor 16 for the first mill stand 4 is connected in seriescircuit which contains a series field 83, commutating field 84, and thearmature of the booster generator 17. The series circuit is connectedacross the supply leads 1-4 and 15. The booster generator 17 has atapped main field '85 and an auxiliary field 86. The booster generator17 is provided to compensate for the 1R drop in the circuit of thearmature of the motor 16, and, therefore, the excitation of its mainfield winding 85 must be a function of the magnitude and sense of the IRdrop in that circuit. This is accomplished by co-nnecting the IRcompensating windings '72 and 79 of the magnetic amplifiers 64 and 65 inseries with each other across the commutating field 84 of the drivemotor 16. Thus, if the voltage drop across the commutating field 84 isof the polarity shown, a current will flow through the IR compensatingwindings 79 and '72 in the direction indicated. If the voltage dropacross the commutating field 84 is opposite to the polarity shown, whichwould occur on regeneration or reverse rotation of the motor 16, currentwould fiow through the circuit in the opposite direction. The IRcompensation control windings 72 and 79 are wound such that when acurrent flows through the windings in the direction indicated, the coreof the magnetic amplifier 65 will be driven toward saturation and themagnetic amplifier 64 will be driven toward cutoff and when the currentfiows in the direction opposite to that shown, the core of magneticamplifier 64 will be driven toward saturation while the magneticamplifier 65 will be driven toward cutoif.

The control windings 73 and 80 of the magnetic amplifiers 64 and 65 areconnected to receive energization supplied from the output of the firstmagnetic amplifier stage across the mixing resistors 54 and 55. Thecircuit comprises a blocking rectifier 93 and mixing resistor 94connected in series with mixing resistor 95 and the blocking rectifier96 across the terminals of the mixing resistors 54 and 55. The controlwinding 80 of the magnetic amplifier 65 is connected in series with arectifier 97 across the series combination of the blocking rectifier 93and the mixing resistor 94 and the control winding 73 of the magneticamplifier 64 is connected in series with the rectifier 93 across theseries combination of the mixing resistor 95 and the blocking rectifier96. The blocking rectifiers 93 and 96 are oppositely poled such that ifthe upper terminal on the mixing resistor 54 were positive with respectto the lower terminal on the mixing resistor 55, a current would flowfrom the upper terminal of the mixing resistor 54 through the rectifier97, control winding 80, mixing resistor 95 and the blocking rectifier 96to the lower terminal of the mixing resistor 55. This condition existswhen the tension in the strip of material 2 is greater than thatselected by the reference source. When the tension in the strip is lessthan that selected by the reference source, the lower terminal of themixing resistor 55 will be positive with respect to the upper terminalof the mixing resistor 54 and a current will flow from the lowerterminal of the mixing resistor 55 through the rectifier 98, the controlwinding 73 of the magnetic amplifier 64, the mixing resistor 94, and theblocking rectifier 93 to the upper terminal of the mixing resistor 54.The circuit of each of the control windings 73 and 80 is poled'in such adirection that a current flowing in either winding will drive the coreon which the respective winding is wound toward saturation. If thetension in the strip of material 2 is that which is selected by thereference source, current will not flow in either of the controlwindings '73 or 80 of the second stage magnetic amplifiers 64 and 65,and therefore the second magneticamplifier stage 21 will simply act tocompensate for the IR drop in the circuit of the armature of the drivemotor 16.

It has already been demonstrated how the IR compensating windings 72 and79 of the second stage magnetic amplifiers 64 and 65, respectively,control the output of their respective amplifiers in accordance with thearmature current of the drive motor 16. The output of the magneticamplifier 65 will appear across the output terminals of the full wavebridge rectifier 82. The output terminals of the full wave bridgerectifier 82 are connected across one half of the main field winding 85of the booster generator 17, and, therefore, the output of the magneticamplifier 65 controls the excitation of the booster generator 17. Theportion of the field winding 85 which is connected across the outputterminals of the full wave bridge rectifier 82 is wound in such adirection and connected to full wave bridge rectifier 82 in such amanner that an increase of voltage across the output terminals of thefull wave bridge rectifier 82 increases the excitation of the boostergenerator 17, and thus increases the voltage generated by the boostergenerator in the sense shown.

Thus, if the IR drop across the commutating field 84 increases in thesense shown, an increased current flows in the direction shown throughthe IR compensating windings 79 and 72 of the magnetic amplifiers 65 and64 respectively, which causes the output of the magnetic amplifier 65 toincrease and as a consequence, the voltage across the output terminalsof the full wave bridge rectifier 82 to increase, thus increasing theexcitation of the booster generator 17. Under these conditions, thevoltage of the booster generator 17 increases to compensate for theincreased IR drop in the armature circuit of the motor 16.

The output terminals of the full wave bridge rectifier 81 are connectedacross the remaining half of the field winding 85 of the boostergenerator 17, and the connection is such that an output from the fullwave bridge rectifier 81 reduces the excitation of the booster generator17 to reduce its output or, under certain conditions, causes the outputof the booster generator 17 to reverse polarity.

It will be appreciated from the above discussion that IR compensation isprovided for the armature circuit of the drive motor 16 regardless ofthe direction of rotation of the motor and regardless of whether thecurrent in the circuit is in the normal sense for the given direction ofrotation or regenerative as on braking.

The auxiliary field winding 36 of the booster generator 17 is connectedin series with an adjustable resistor 99 across the two anti-huntdamping windings 38 and 45 of the first magnetic amplifier stage 20. Theauxiliary field winding 86 provides a signal which is substantiallyproportional to the rate of change of the booster generated voltage.This stems from the fact that the winding 86 is magnetically coupledwith field 85 which produces the excitation flux. This is a D. C. flux.Hence, under steady state conditions, when the excitation flux isconstant, no voltage is induced in winding 86. Under transientconditions the ampere turns of field 85 are varied by the magneticamplifier and the excitation fiux correspondingly changes. The rate ofchange of the excitation flux induces a voltage in winding 86. Since theoutput voltage of the booster generator is proportional to theexcitation flux, the rate of change of the output voltage isapproximately proportional to the rate of change of the excitation flux,and the voltage of winding 86 is proportional to the rate of change ofthe booster generator voltage. Since the voltage of winding 86 is fedback to the first magnetic amplifier stage 20, it provides a powerfuldamping effect. The adjustable resistor 99 and capacitor 92 form an RCdelay network in the anti-hunt damping feedback loop. The anti-huntdegeneration windings 70 and 46 of the first magnetic amplifier stage 24are connected in series with each other and an adjusting potentiometer100 directly across the main field winding 85 of the booster generator17. Thus, a degenerative feedback is provided around the two stages ofthe magnetic amplifier. This feedback not only improves stability, butserves to linearize the transfer characteristics of the magneticamplifier.

It has already been described how a strip tension which is greater thanthat selected by the reference voltage causes a current to circulatethrough the control winding 80 of the magnetic amplifier 65, and thiscauses an increase of the output of the magnetic amplifier 65. Thus, thevoltage across the-output terminals of the full wave bridge rectifier 82increases. The excitation of the booster generator 17 is increased andthus the voltage generated by the booster generator 17 is increased tocause a motoring current to flow in motor 16. Consequently, the drag ofthe first mill stand is reduced to reduce the tension of the strip ofmaterial 2. Conversely, when the tension is less than that selected bythe reference voltage, a current will circulate in the control winding73 of the second stage magnetic amplifier 64 to reverse the excitationof the main field winding and thereby reverse the voltage of the boostergenerator 17, thus causing a regenerating current to flow in the drivemotor 16 of the first mill stand. This causes the drag of the first millstand to increase, and to increase the tension in the strip of material2.

When threading the strip of material into the mill, it is necessary toremove the regulation from the system. Otherwise, there would be notension signal on the tension control windings 41 and 48 of the firstmagnetic amplifier stage 20 and the reference signal would have itsmaximum effect on the first magnetic amplifier stage to cause the motorof the first mill stand to slow down, stop or even reverse dependingupon the limits of the regulating system, while the second mill standwould be rotating at normal speed. The same would hold true in the eventthat the strip of material between the first and second mill standsshould break, the first stand motor would slow down immediately. Inorder that the threading operation may be accomplished without thetension regulation, a magnetic amplifier relay circuit 26 is provided.The voltage sensitive magnetic relay circuit is shown and described indetail in a copending application of Arthur 0. Fitzner, Serial No.378,585, filed September 4, 1953, entitled Electrical Control Apparatusand assigned to the assignee of this invention. The magnetic amplifierrelay circuit 26 comprises the magnetic amplifier 118 which has itscircuits connected in a conventional doubler arrangement. The magneticamplifier has main windings 111 and 112-. The main winding 111 isconnected in series with the saturating rectifier 113 and the mainwinding 112 is connected in series with the saturating rectifier 114,and the two series circuits are connected in parallel. The magneticamplifier 110 is provided with a control winding 115, a biasing winding116 and a feedback winding 117. The magnetic amplifier 110 is suppliedfrom a transformer T5 which is connected across two leads L1 and L2 ofan alternating current source. One terminal of the transformer T5 isconnected to a point between the saturating rectifiers 113 and 114, andanother terminal is connected to an input terminal of the full wavebridge rectifier 118. The opposite input terminal of the full wavebridge rectifier 118 is connected to a point between the two mainwindings 111 and 1120f the magnetic amplifier 110. The biasing winding116 is connected in series with an adjusting resistor 119 across theoutput terminals of a full wave bridge rectifier 120, the inputterminals of which are connected across the secondary winding terminalsof the transformer T5. The feedback winding 117 is connected directlyacross the output terminals of the bridge rectifier 118 and is connectedfor positive feedback. The control Winding of the magnetic amplifier 110is connected directly across the mixing potentiometer 34 which receivesthe resultant output voltage generated by the tensiometer 5.

An electromagnetic relay 121 has its coil 122 connected directly acrossthe output terminals of the full wave bridge 118 to receive the outputof the magnetic amplifier 110. The electromagnetic relay 121 and themagnetic amplifier 110 have their characteristics matched such that theelectromagnetic relay 121 will only be picked up when there is a signalgenerated by the tensiometer 5 which occurs only when strip isoperatively passing between the first and second mill stands.

The transformers T1, T2, T3 and T4 which supply the energization for thefirst and the second magnetic amplifier stages 20 and 21,. respectively,are connected to be energized from the alternating current buses L1 andL2. The transformers T1 and T2 which supply the source for the magneticamplifiers 35 and 36 of the first stage are connected to the sourcethrough a hand switch S1 and contacts 123 of the electromagnetic relay121. Thus, when the tensiometer 5 generates a signal, the magneticamplifier 116 has an output which will energize the coil 122 of theelectromagnetic relay 121, and cause it to close its contacts 123 to putthe first magnetic amplifier stage 26 in the system. Under theseconditions, the system operates as previously described. However, whenthe strip of material 2 is not opera-ti-vely passing through the mill,the electromagnetic relay 121 is not picked up and the first magneticamplifier stage is effectively eliminated from the system. Thus, thedriving motor 16 for the first mill stand can be operated as desiredwithout the tension regulation but, with the 1R compensation provided bythe second magnetic amplifier stage 21. For

the threading operation, it is desirable that an appreciable amount ofIR compensation be applied on the first mill stand to prevent stalling.This is accomplished since the IR compensation signal from thecommutating field 84 is fed back to the second magnetic amplifier stageas described. The speed of response of this IR compensation is increasedfor the threading operation since removal of the first magneticamplifier stage 20 from the system effectively removes the damping fromthe system.

When the electromagnetic relay 121 is energized it alsocloses itscontacts 89 to bypass apart of the adjusting resistor F119 and increasethe bias of the magnetic amplifier. This renders the magnetic amplifierrelay circuit 26 voltage sensitive as described in the copending.application of Arthur 0. Fitzner previously referred to.

it may be seen that the objects of this invention have been accomplishedby providing atension regulating and control system which gives positiveand precise control of the strip tension between the first two stands ofa mill, and which allows the first stand to be controlled as desiredwithout tension regulation when the strip of material is not operativelypassing between the mill stand.

Although one embodiment of this invention has been shown and describedin detailin compliance with the patent statutes, it is to beparticularly understood that the invention is not limited thereto orthereby, but that equivalents are clearly within the inventive scope.

We claim as our invention: 7 I

1 A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising, afirst and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, first and second individual sets of fieldwindings for said generator, at least one magnetic amplifier stageconnected to energize said first set of field windings, means forsupplying a flux to the magnetic amplifier cores of said magneticamplifier stage in accordance with the difference in a reference signaland a signal which is a function of the tension in the strip of materialbetween the two rolls, said second individual set of field windings forsaid generator being connected to control means for said magneticamplifier stage to supply said magnetic amplifier cores in accordancewith the rate of change of voltage of said generator.

2. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising, a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, first and second individual sets of fieldwindings for said generator,- at

least one magnetic amplifier stage connected to energize said first setof field windings, first, second, and third control windings for theindividual magnetic amplifiers of said magnetic amplifier stage, saidfirst individual control windings being connected to receive a referencevoltage, said second individual control windings being connected toreceive a signal which is a function of the tension of the strip ofmaterial, said first and second control windings being wound in such amanner and connected to their respective sources in such a manner as tohave opposing effects on the saturation of the magnetic amplifiers, saidthird individual control means being connected to said second individualset of field windings for said generator to receive a signal which is afunction of the rate of change of generator voltage.

3. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising, a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, first and second individual sets of controlwindings for said generator, at least two magnetic amplifier stagesconnected to energize said first set of field windings, the output ofsaid first magnetic amplifier stage being connected to determine theoutput of said second magnetic amplifier stage, first, second, third,and fourth control windings for the individual magnetic amplifiers ofsaid first magnetic amplifier stage, said first individual controlwindings being connected to receive a reference voltage, said secondindividual control windings being connected to receive a signal which isa function of the tension of the strip of material, said first andsecond control windings being wound in such a manner and connected totheir respective sources in such a manner as to have opposing efiects onthe saturation of the magnetic amplifiers, said third individual controlmeans being connected to said second individual set of field windingsfor said generator to receive a signal which is a function of the rateof change of generator voltage, said fourth individual control meansbeing connected to receive a signal which is porportional to the outputof said second magnetic amplifier stage, said signal being of suchpolarity and said fourth individual control windings being wound upontheir respective cores in such a manner that the signal will have adegenerative effect on the output of the magnetic amplifier stages.

4. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising, a motorconnected indriving relation with one roll, a controlled motor connectedin driving relation with the other roll, a generator connected incircuit relationship with said controlled motor, excitation means forsaid generator, at least one magnetic amplifier stage, said excitationmeans for said generator being connected to receive its energizationfrom the output of said magnetic amplifier stage, and means fordetermining the output of said magnetic amplifier stage in accordancewith the current in the motor armature circuit and the differencebetween a reference signal and a signal which is a function of thetension in the strip of material.

5. A control system for a tension device having apair of rolls betweenwhich a strip' of material is disposed to pass comprising, a first andaseeond electric motor each connected in driving relation with one ofthe pair of rolls, said first and second motors adapted to be connected'across a power source, a generator connected in circuit relationshipwith said first motor, excitation means for said generator, at least onemagnetic amplifier stage, said excitation means for said generator beingconnected to receive its energization from the output magnetic amplifier stage, means for selectively determining the output of theoutput magnetic amplifier stage in accordance with the current in themotor armature circuit and the difference in a reference signal and asignal which is a function of the tension in the strip of material whenthe strip is operatively passing between the rolls and determining theoutput of the output magnetic amplifier stage in accordance with thecurrent in the motor armature circuit only when the strip of material isnot operatively passing between the two rolls.

6. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising, a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, excitation means for said generator, at least onemagnetic amplifier stage, said excitation means for said generator beingconnected to receive its energization from the output magnetic amplifierstage, means for selectively determining the output of the outputmagnetic amplifier stage in accordance with the current in the motorarmature circuit and the difference in a reference signal and a signalwhich is a function of the tension in the strip of material when thestrip is operatively passing between the rolls and determining theoutput of the output magnetic amplifier stage in accordance with thecurrent in the motor armature circuit and decreasing the response timethereto only when the strip of material is not operativeiy passingbetween the two rolls.

7. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising, a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, first and second individual sets of controlwindings for said generator, at least two magnetic amplifier stagesconnected to energize said first set of field windings, first, second,third, and fourth control windings for the individual magneticamplifiers of said first magnetic amplifier stage, said first individualcontrol windings being connected to receive a reference voltage, saidsecond individual control windings being connected to receive a signalwhich is a function of the tension of the strip of material, said firstand second control windings being wound in such a manner and connectedto their respective sources in such a manner as to have opposing effectson the saturation of the magnetic amplifiers, said third individualcontrol means being connected to said second individual set of fieldwindings for said generator to receive a signal which is a function ofthe rate of change of generator voltage, the output of said firstmagnetic amplifier stage being connected to determine the output of saidsecond magnetic amplifier stage, first, second, third, and fourthcontrol windings for the individual magnetic amplifiers of said firstmagnetic amplifier stage, said first individual control windings beingconnected to receive a reference voltage, said second individual controlwindings being connected to receive a signal which is a function of thetension of the strip of material, said first and second control windingsbeing wound in such a manner and connected to their respective sourcesin such a manner as to have opposing effects on the saturation of themagnetic amplifiers, said third individual control means being connectedto said second individual set of field windings for said generator toreceive a signal which is a function of the rate of change of generatorvoltage, said fourth individual control means being connected to receivea signal which is proportional to the output of said second magneticamplifier stage, said signal being of such polarity and said fourthindividual control windings being wound upon their respective cores insuch a manner that the signal will have a degenerative effect on theoutput of the magnetic amplifier stages, first and second controlwindings for said second stage magnetic amplifiers, said first controlwindings being connected to receive the output of the first stage ofmagnetic amplifiers and said second control windings for said secondstage of magnetic amplifiers being connected to receive a signal whichis a function of current in the motor armature circuit.

8. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising, a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, first and second individual sets of controlwindings for said generator, at least two magnetic amplifier stagesconnected to energize said first set of field windings, first, second,third, and fourth control windings for the individual magneticamplifiers of said first magnetic amplifier stage, said first individualcontrol windings being connected to receive a reference voltage, saidsecond individual control windings being connected to receive a signalwhich is a function of the tension of the strip of material, said firstand second control windings being wound in such a manner and connectedto their respective sources in such a manner as to have opposing etfectson the saturation of the magnetic amplifiers, said third individualcontrol means being connected to said second individual set of fieldwindings for said generator to receive a signal which is a function ofthe rate of change of generator voltage, the output of said firstmagnetic amplifier stage being connected to determine the output of saidsecond magnetic amplifier stage, first, second, third, and fourthcontrol windings for the individual magnetic amplifiers of said firstmagnetic amplifier stage, said first individual control windings beingconnected to receive a reference voltage, said second individual controlwindings being connected to receive a signal which is a function of thetension of the strip of material, said first and second control windingsbeing wound in such a manner and connected to their respective sourcesin such a manner as to have opposing effects on the saturation of themagnetic amplifiers, said third individual control means being connectedto said second individual set of field windings for said generator toreceive a signal which is a function of the rate of change of generatorvoltage, said fourth individual con trol means being connected toreceive a signal which is proportional to the output of said secondmagnetic amplifier stage, said signal being of such polarity and saidfourth individual control windings being wound upon their respectivecores in such a manner that the signal will have a degenerative effecton the output of the magnetic amplifier stages, first and second controlwindings for said second stage magnetic amplifiers, said first controlwindings being connected to receive the output of the first stage ofmagnetic amplifiers and said second control windings for said secondstage of magnetic amplifiers being connected to receive a signal whichis a function of current in the motor armature circuit and means forremoving the first stage of magnetic amplifiers from the system when thestrip of material is not operatively passing between the pair of rolls.

9. A control system for a tension device having a pair of rolls betweenwhich a trip of material is disposed to pass comprising, a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, first and second indi vidual sets of controlwindings for said generator, at least two magnetic amplifier stagesconnected to energize said first set of field windings, first, second,third, and fourth control windings for the individual magneticamplifiers of said first magnetic amplifier stage, said first individualcontrol windings being connected to receive a reference voltage, saidsecond individual control windings being connected to receive a signalwhich is a function of the tension of the strip of material, said firstand second control windings being wound in such a manner and connectedto their respective sources in such a manner as to have opposing effectson the saturation of the magnetic amplifiers, said third individualcontrol means being connected to said second individual set of fieldwindings for said generator to receive a signal which is a function ofthe rate of change of generator voltage, the output of said firstmagnetic amplifier stage being connected to determine the output of saidsecond magnetic amplifier stage, first, second, third, and fourthcontrol windings for the individual magnetic amplifiers of said firstmagnetic amplifier stage, said first individual control windings beingconnected to receive a reference voltage, said second individual controlwindings being connected to receive a signal which is a function ofthevtension of the strip of material, said first and second controlwindings being wound in such a manner and connected to their respectivesources in such a manner as to have opposing effects on the saturationof the magnetic amplifiers, said third individual control means beingconnected to said second individual set of field windings for saidgenerator to receive a signal which is a function of the rate of changeof generator voltage, said fourth individual control means beingconnected to receive a signal which is proportional to the output ofsaid second magnetic amplifier stage, said signal being of such polarityand said fourth individual control windings being wound upon theirrespective cores in such a manner that the signal will have adegenerative effect on the output of the magnetic amplifier stages,first and second control windings for said second stage magneticamplifiers, said first control windings being connected to receive theoutput of the first stage of magnetic amplifiers and said second controlwindings for saidsecond stage of magnetic amplifiers being connected toreceive a signal which is a function of current in the motor armaturecircuit, a relay magnetic amplifier connected to have its outputdetermined by the signal which is a measure of tension in the strip ofmaterial, said relay magnetic amplifier being adapted to cause saidfirst stage of magnetic amplifiers to be effectively removed from thesystem until the signal which is a measure of tension in the strip is ofa predetermined magnitude.

10. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising, a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, first and second individual sets of controlwindings for said generator, at least two magnetic amplifier stagesconnected to energize said first set of field windings, first, second,third, and fourth control windings for the individual magneticamplifiers of said first magnetic amplifier stage, said first individualcontrol windings being connected to receive a reference voltage, saidsecond individual control windings being connected to receive a signalwhich is a function of the tension of the strip of material, said firstand second control windings being wound in such a manner and connectedto their respective sources in such a manner as to have opposing effectson the saturation of the magnetic amplifiers, said third individualcontrol means being connected to said second individual set of fieldwindings for said generator to receive a signal which is a function ofthe rate of change of generator voltage, the output of said firstmagnetic amplifier stage being connected to determine the output of saidsecond magnetic amplifier stage, first, second, third, and fourthcontrol windings for the individual magnetic amplifiers of said firstmagnetic amplifier stage, said first individual control windings beingconnected to receive a reference voltage, said second individual controlwindings being connected to receive a signal which is a function of thetension of the strip of material, said first and second control windingsbeing wound in such a manner and connected to their respective sourcesin such a manner as to have opposing effects on the saturation of themagnetic amplifiers, said third individual control means being connectedto said second individual set of field windings for said generator toreceive a signal which is a function of the rate of change of generatorvoltage, said fourth individual control means being connected to receivea signal which is proportional to the output of said second magneticamplifier stage, said signal being of such polarity and said fourthindividual control windings being wound upon their respective cores insuch a manner that the signal will have a degenerative effect on theoutput of the magnetic amplifier stages, first and second controlwindings for said second stage magnetic amplifiers, said first controlwindings being connected to receive the output of the first stage ofmagnetic amplifiers and said second control windings for said secondstage of magnetic amplifiers being connected to receive a signal whichis a function of current in the motor armature circuit, a relay magneticamplifier connected to have its output determined by the signal which isa measure of tension in the strip of material, a relay having anenergizing means and contact means, the energizing means for said relaybeing connected to receive the output of said relay magnetic amplifierand the contacts of said relay being, adapted to selectively disconnectand connect the first stage of magnetic amplifiers and the system whenin the deenergized and energized conditions respectively.

11. A control system for a tension device having a pair of rolls betweenwhich a strip of materialis disposed to pass comprising a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, a first and a second stage of magneticamplifiers, excitation means for saidgenerator connected to be suppliedby the second stage of magnetic amplifiers, the second stage of magneticamplifiers connected to have its output controlled in accordance withthe output of said first magnetic amplifier stage and the current in thearmature circuit of the first electric motor, the first stage ofmagnetic amplifiers being connected to have its output controlled inaccordance with a signal which is the difference between a referencesignal and a signal which is a function of the tension in the strip ofmaterial, and a relay means for selectively connecting the first stageof magnetic amplifiers and the system when the strip of material isoperatively passing between the pair of roll stands and disconnectingthe first stage of magnetic amplifiers from the system when the strip ofmaterial is not operatively passing between the pair of roll stands.

12. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising a first and asecond electric motor each r connected in driving relation with one ofthe pair of rolls,

said first and second motors adapted to be connected across a powersource, a generator connected in circuit relationship with said firstmotor, a first and a second stage of magnetic amplifiers, excitationmeans for said generator connected to be supplied by the second stage ofmagnetic amplifiers, the first stage of magnetic amplifiers beingconnected to have its output controlled in accordance with a signalwhich is the difference between a reference signal and a signal which isa function of the tension in the strip of material, and a relay meansfor selectively connecting the first stage of magnetic amplifiers andthe system when the strip of material is operatively passing between thepair of roll stands and disconnecting the first stage of magneticamplifiers from the system when the strip of material is not operativelypassing between the pair of roll stands.

13. A tension control system for a tension device use with a mill havinga pair of rolls between which a strip of material is disposed to passcomprising, a motor connected in driving relation with one roll, acontrolled motor connected in driving relation with the other rollstand, a generator connected in circuit relationship with saidcontrolled motor, excitation means for said generator, at least oneamplifier stage, said excitation means for said generator beingconnected to receive its energization from the output amplifier stage,and means for determining the output of the output amplifier stage inaccordance with the current in the controlled motor armature circuit andthe difference in a reference signal and a signal which is a function ofthe tension in the strip of material.

14. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising, a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, excitation means for said generator, at least oneamplifier stage, said excitation means for said generator beingconnected to receive its energization from the output magnetic amplifierstage, means for selectively determining the output of the outputamplifier stage in accordance with the current in the motor armaturecircuit and the difierence in a reference signal and a signal which is afunction of the tension in the strip of material when the strip isoperatively passing between the rolls and determining the output of theoutput amplifier stage in accordance with the current in the motorarmature circuit only when the strip of material is not operativelypassing between the two rolls.

15. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, a first and a second stage of amplifiers,excitation means for said generator connected to be supplied by thesecond stage of amplifiers, the second stage of amplifiers connected tohave its output controlled in accordance with the output of said firstamplifier stage and the current in the armature circuit of the firstelectric motor, the first stage of amplifiers being connected to haveits output controlled in accordance with a signal which is thedifference between a reference signal and a signal which is a functionof the tension in the strip of material, and a relay means forselectively connecting the first stage of amplifiers and the system whenthe strip of material is operatively passing between the rolls anddisconnecting the first stage of magnetic amplifiers from the systemwhen the strip of material is not operatively passing between the tworolls.

16. A control system for a tension device having a pair of rolls betweenwhich a strip of material is disposed to pass comprising a first and asecond electric motor each connected in driving relation with one of thepair of rolls, said first and second motors adapted to be connectedacross a power source, a generator connected in circuit relationshipwith said first motor, a first and a second stage of amplifiers,excitation means for said generator connected to be supplied by thesecond stage of amplifiers, the first stage of amplifiers beingconnected to have its output controlled in accordance with a signalwhich is the difference between a reference signal and a signal which isa function of the tension in the strip of material, and a relay meansfor selectively connecting the first stage of magnetic amplifiers andthe system when the strip of material is operatively passing between therolls and disconnecting the first stage of magnetic amplifiers from thesystem when the strip of material is not operatively passing between thetwo rolls.

References Cited in the file of this patent UNITED STATES PATENTS

